Field
This disclosure relates to producing components using composite materials, such as by controlling the application of tows of composite material during an automated fiber placement operation.
Description of the Related Art
Composite materials are used for a variety of high-performance applications, such as in aerospace components, automotive parts, and sporting goods A composite material includes at least two constituent materials that are combined to produce a material with characteristics significantly different than the constituent materials individually. Composite materials typically include a bonding agent or matrix (e.g., a glue or resin) and a substrate or reinforcement (e.g., fiberglass, graphite, carbon-fiber, or other fibrous material). Layers of the composite material can be applied to a form that represents the shape of a component, such as a fuselage, turbine cowling, or wing. The composite material is then cured, during which the bonding agent liquefies and flows through the layers of the substrate. The result is a single coherent structure with an excellent strength to weight ratio.
Certain composite components are produced by layering the composite material onto the form with a hand layup technique. This includes cutting flat patterns of composite material and then manually placing or pressing those patterns onto the form. Hand layup requires that the shape of each layer of material be converted from the 3-dimensional piece to be produced into a flat pattern, so that the pattern can be cut. It also requires great amounts of manual labor to orient and apply the patterns to the form.
An advance over hand layup is tape layup, which includes using a machine to apply wide strips (called “tape”) of composite material to the form. Typically, the tape is between 25 mm and 200 mm wide and is stored on a spool. During application, the tape travels from the spool to a compaction roller, which presses the material onto the form or onto the previous layers of material. Generally, the compaction roller is mounted on a computer-controlled 5-axis machine (e.g., a CNC machine with the compaction roller instead of a milling cutter). The tape is pulled onto the form by the compaction roller being rolled over the surface of the form. To aid in maintaining the tape in place until curing, the tape can be heated during application and/or can have an adhesive on at least one side. When the tape is applied to a curved surface, one lateral side of the tape experiences compression and the opposite lateral side of the tape experiences tension. This can result in wrinkling, tearing, or warping of the tape and can be exacerbated by the relatively wide width of the tape. Thus, tape layup is typically limited to regular, smooth, and/or relatively flat shapes, such as wing surfaces and cylindrical missile sections.
An advance over tape layup is automated fiber placement (AFP), which includes using a machine to apply rows (called “courses”) that are each made up of multiple narrow strips (called “tows”) of the composite material. For example, each course can include between 8 and 32 tows, and each tow can be between 3 mm and 12 mm wide. Typically, several tows pass over a compaction roller (also called a “head”) generally parallel to each other and can be concurrently applied to a form having the shape of the component to be produced. The compaction roller can be moved relative to the form to steer the application of the tows to a desired area of the form, to provide a desired application pattern of the tows, or otherwise. The application of each tow to the form can be controlled independent of the other tows. For example, each tow can be individually started, stopped, cut, and/or restarted.